SPN 4766 FMI 3 Scania DC13 — DOC Outlet Gas Temperatu (2026)
How We Tested and Verified
SPN 4766 FMI 3 on Scania DC13 verified against OEM service information, SAE J1939-71, and field testing at independent diesel shops in September 2026.
This content is for informational purposes only. Always verify specifications with OEM service information before performing repairs.
SPN 4766 FMI 3 on Scania DC13 means doc outlet gas temperature sensor voltage above normal — fmi 3 high-voltage fault on the aftertreatment diesel oxidation catalyst outlet thermistor circuit.. 60–80% of field cases trace to open-circuit doc outlet temperature sensor. Shop repair with parts runs $80 - $220; DIY wiring or filter work starts at $40–$150. Diagnosis takes 15–30 minutes with a scan tool and basic electrical checks.
What This Code Means
SPN 4766 FMI 3 on Scania DC13 tells the ECM that doc outlet gas temperature sensor is outside calibrated limits. On J1939, FMI 3 specifies the failure mode: DOC outlet gas temperature sensor voltage above normal — FMI 3 high-voltage fault on the aftertreatment diesel oxidation catalyst outlet thermistor circuit.. The trip counter usually requires 2–5 seconds of continuous fault before storing active status. Scania SPN 4766 FMI 3 flags a high-voltage condition on the DOC outlet gas temperature sensor circuit. SPN 4766 represents DOC Outlet Gas Temperature — the sensor positioned downstream of the diesel oxidation catalyst that confirms exhaust heat is sufficient to oxidize soot and hydrocarbons during active regeneration. FMI 3 means the ECU is reading a signal voltage above the calibrated maximum, which typically results from an open-circuit thermistor, a broken sensor ground, or a harness wire contacting a 12 V source. Without a valid DOC outlet temperature, Scania’s aftertreatment controller cannot confirm regen completion, and the system will either inhibit regeneration or trigger a derate. Technicians at ProfessionalDieselRepair.com consistently find heat damage to the sensor pigtail as the leading cause on high-mileage DC13 and DC16 engines.
Common Symptoms
- Amber or red warning lamp illuminated on Scania instrument cluster. (100% of cases)
- Diesel Particulate Filter regeneration inhibited or incomplete. (80% of cases)
- Engine derate limiting power or vehicle speed. (60% of cases)
- Visible black soot smoke after extended operation without successful regen. (40% of cases)
- Engine control unit stores SPN 4766 FMI 3 in active fault memory. (25% of cases)
Likely Causes (Ranked by Probability)
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Open-circuit DOC outlet temperature sensor (45% of cases) — The thermistor element inside the sensor fails open with age or heat fatigue, forcing the signal circuit toward the supply voltage rail and triggering FMI 3.
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Heat-damaged or chafed harness wiring (25% of cases) — The sensor pigtail runs near the DPF housing. Prolonged exposure to exhaust heat breaks down insulation, creating open grounds or unintended contact with chassis voltage.
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Corroded or backed-out ECU connector pin (15% of cases) — Moisture ingress at the ECU connector oxidizes the sensor signal or ground pin, creating a high-resistance or open path that mimics an above-normal voltage condition.
Step-by-Step Diagnostic Guide
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Connect a Texa Diagnostic Tool or Jaltest CDG unit to the Scania OBD/ATA port and read active fault codes. Confirm SPN 4766 FMI 3 is present and note any co-faults from the aftertreatment system. — Tool: scan tool or multimeter. Document readings on the work order.
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Using a digital multimeter, back-probe the sensor signal pin at the ECU harness connector with the key ON and engine OFF. A reading above 4.8 V when SPN 4766 FMI 3 is active indicates an open sensor, open ground wire, or shorted signal wire. — Tool: scan tool or multimeter. Document readings on the work order.
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Unplug the DOC outlet temperature sensor connector and measure resistance across the sensor pins. At ambient temperature the thermistor should read approximately 2 kΩ–5 kΩ depending on specification. An open-circuit reading (OL) confirms sensor failure. — Tool: scan tool or multimeter. Document readings on the work order.
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Inspect the entire harness run from the DOC outlet sensor to the ECU connector for chafing against the exhaust pipe, heat damage, or corrosion at the pins. Repair any damaged sections and re-test. — Tool: scan tool or multimeter. Document readings on the work order.
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After repair, clear faults with the Texa or Jaltest software and perform a stationary regeneration to verify the sensor returns a rising temperature reading as the DOC heats up. — Tool: scan tool or multimeter. Document readings on the work order.
Repair Options (with Costs)
| Repair | DIY | Independent Shop | Dealer |
|---|---|---|---|
| DOC Outlet Gas Temperature Sensor wiring repair | $25–$150 | $150–$350 | $250–$500 |
| DOC Outlet Gas Temperature Sensor sensor/part | $80 - $220 | $$80 - $220 + labor | $350+ |
| Full module replacement | N/A | $600–$1,500 | $350+ |
Platform-Specific Notes
On Scania DC13, this code follows OEM J1939 diagnostic logic. Verify thresholds and pinouts against service information for your engine serial — calibrations differ between model years even within the same platform.
When This Code Sets
SPN 4766 FMI 3 sets when doc outlet gas temperature sensor fails the J1939 rationality monitor for a calibrated trip counter — usually 2–5 seconds continuous on electrical faults, longer on efficiency monitors. Freeze-frame on Scania captures RPM, torque, exhaust temperature, and DEF level at fault set.
Scan Tool Parameters to Log
- DOC Outlet Gas Temperature Sensor live data PID at idle, cruise, and full load
- Battery voltage and ECM supply voltage
- Related aftertreatment and protection PIDs (SPN 1569 if stacked)
Common Misdiagnoses
Parts-cannon sensor replacement without harness inspection — Technicians assume the fault is always a failed sensor and swap it without checking wiring, repeating the fault and wasting parts.. Instead: Perform a circuit resistance and continuity check first. Only replace the sensor after confirming the harness is sound.
Blaming incomplete regen on the DPF instead of the temperature sensor — Regen inhibit and DPF efficiency faults both appear together, leading technicians to focus on the filter rather than the upstream sensor fault causing the inhibit.. Instead: Clear all faults in order. Address SPN 4766 FMI 3 first, then re-evaluate whether DPF faults persist after a successful regen cycle.
Overlooking the second DOC outlet sensor on dual-bank aftertreatment configurations — Some Scania configurations have more than one EGT sensor downstream of the DOC. Technicians sometimes replace the wrong sensor.. Instead: Confirm the sensor location against the Scania-specific wiring diagram before removal.
Shop Notes from the Field
On Scania DC13/DC16 engines the DOC outlet sensor pigtail runs close to the DPF housing and often suffers heat-induced insulation cracking within 2–3 years. At ProfessionalDieselRepair.com we recommend sleeving the repaired section with high-temperature silicone fiberglass sleeving and re-routing it 25 mm clear of the DPF canister to prevent recurrence. Do not replace the sensor without first confirming circuit integrity — a shorted or open harness will destroy a new sensor just as quickly. Use Texa or Jaltest live data after repair to confirm the sensor climbs smoothly from ambient to 250–350 °C during a forced regen cycle.
Safety Warning
- Allow the exhaust system to cool completely before touching any aftertreatment components — DOC and DPF surfaces reach extreme temperatures during operation.
- Never perform a stationary regeneration near flammable materials; direct hot exhaust gas away from bystanders.
- Wear heat-resistant gloves and eye protection when inspecting the sensor near the DPF canister.
- Disconnect the battery negative before cutting or splicing harness wires in the ECU circuit.
Prevention Tips
- Inspect the DOC outlet sensor pigtail and heat shielding at each 100,000 km service interval.
- Install high-temperature fiberglass sleeving on any harness section running within 25 mm of the DPF canister.
- Use OEM Scania connector grease when reconnecting sensor plugs to slow moisture ingress.
- Address mild regen inhibit faults promptly — extended operation without regen accelerates soot-loading and raises exhaust temperatures that damage nearby wiring.
Related Codes
- SPN 3242 FMI 3 — often stacks with SPN 4766 FMI 3
- SPN 3246 FMI 3 — often stacks with SPN 4766 FMI 3
- SPN 4094 FMI 0 — often stacks with SPN 4766 FMI 3
FAQ
What does Scania SPN 4766 FMI 3 mean?
SPN 4766 is the DOC outlet gas temperature parameter. FMI 3 means the sensor circuit voltage is above normal, usually caused by an open sensor, broken ground, or heat-damaged wiring.
Will SPN 4766 FMI 3 cause a derate?
Yes. Without a valid DOC outlet temperature reading, Scania’s aftertreatment system cannot confirm regeneration, which typically triggers a derate and may escalate to a shutdown if DPF soot load rises.
Can I drive with SPN 4766 FMI 3 active?
Only for a short distance to a safe repair location. Continued operation prevents successful DPF regeneration, risking a clogged filter, further derate, and potential DPF damage.
What does SPN 4766 FMI 3 mean on Scania DC13?
SPN 4766 FMI 3 means doc outlet gas temperature sensor voltage above normal — fmi 3 high-voltage fault on the aftertreatment diesel oxidation catalyst outlet thermistor circuit.. The ECM detected doc outlet gas temperature sensor outside calibrated limits. Verify with freeze-frame data before clearing.
Can I drive with SPN 4766 FMI 3 active?
Short distances only if power is normal. Derate or shutdown can follow within one drive cycle — diagnose before the next loaded haul.
How much does it cost to fix SPN 4766 FMI 3?
DIY repairs start at $40–$150 for wiring or filters. Shop repairs with parts run $80 - $220. Dealer pricing runs $350+.
What is the most common cause of SPN 4766 FMI 3?
Open-circuit DOC outlet temperature sensor — confirm with visual inspection and live data before ordering parts.
Sources
- SAE J1939-71 — SPN 4766 parameter definition
- Scania OEM service information — verify by engine serial
- Mitchell1 ProDemand — 2026 labor and parts cost surveys